Size- and ion-selective adsorption of organic dyes from aqueous solutions using functionalized UiO-66 frameworks

Electrostatically Spun Fabrication of Fe3O4@SiO2/PVA Membranes for Efficient Methyl Orange (MO) Adsorption and Response Surface Optimization of the Processes

The environmental pollution problem caused by azo dyes urgently needs to be solved. Fe3O4@SiO2/poly(vinyl alcohol) (PVA) membranes were prepared via an electrostatic spinning process. By blending the prepared Fe3O4@SiO2 nanoparticles with PVA, a uniform distribution of Fe3O4@SiO2 nanoparticles within the fibers was achieved, effectively preventing the aggregation of the nanoparticles and demonstrating excellent adsorption performance toward the azo anionic dye methyl orange (MO). The adsorption isotherms and kinetic data for Fe3O4@SiO2/PVA adsorbed MO were consistent with Langmuir and the pseudo-second-order model, respectively. Owing to the electrostatic attraction, hydrogen bonding, and pore-filling effect, Fe3O4@SiO2/PVA effectively removed MO from water, with a maximum adsorption amount of 349.896 mg/g at 25 °C. Very importantly, the Fe3O4@SiO2/PVA membrane can be regenerated and reused efficiently, with no significant decrease in adsorption capacity after five adsorption cycles. In addition, response surface methodology (RSM) was used to analyze the effects of various factors on the MO adsorption performance of Fe3O4@SiO2/PVA membranes, as well as the interactions of various factors. This research indicated that Fe3O4@SiO2/PVA membranes are promising adsorbents for MO due to their low cost, ease of regeneration, and environmental friendliness.

A Homogeneous Janus Membrane Based on Functionalized MOFs Crosslinked by Aramid Nanofibers for Quasi-Solid-State Lithium Sulfur Batteries

Lithium-sulfur batteries (LSBs) are considered as promising candidates in the next generation of high energy density devices. However, the serious shuttle effect, irreversible dendrite growth of Li metal anode, and the potential safety hazard impede the practical application of LSBs. Herein, a novel homogeneous Janus membrane based on functionalized MOFs crosslinked by aramid nanofibers is designed and synthesized to simultaneously solve the above challenges in quasi-solid-state LSBs. The aramid nanofibers with good mechanical properties and thermal stability act as a homogeneous scaffold to crosslink the MOF particles with different ligands on both sides and this Janus membrane upgrades the stability and safety on both the cathode and anode. Specifically, the amino ligand-decorated MOFs contribute to homogenize Li-ion flux and stabilize the lithium anode, and the sulfonic ligand-decorated MOFs effectively suppress the shuttle effect by the dual effects of chemical adsorption and electrostatic repulsion. The quasi-solid-state LSBs assembled with this homogeneous Janus membrane deliver excellent rate performance and cycling stability. Moreover, it exhibits a high initial capacity of 923.4 mAh g-1 at 1 C at 70 °C, and 697.3 mAh g-1 is retained after 100 cycles, indicating great potential for its application in high-safety LSBs.

Highly graphitized porous carbon/reduced graphene oxide for ultrahigh enrichment and ultrasensitive determination of polycyclic aromatic hydrocarbons

There is an urgent need to develop efficient and reliable coating materials for solid phase microextraction (SPME), in order to quantify and monitor pollutants in environmental waters. Herein, a highly graphitized porous carbon/reduced graphene oxide (PC/rGO) was successfully synthesized by pyrolysis of metal organic framework/graphene oxide precursors, and used as a SPME coating for ultrahigh enrichment of polycyclic aromatic hydrocarbons (PAHs) from water. The as-prepared PC/rGO exhibited high degree of graphitization, abundant number of micro/mesopores along with exceptional thermal stability, making it an ideal SPME coating material. The PC/rGO fiber offered an ultrahigh enrichment factor for PAHs (up to 126057), which could be attributed to the multiple interactions between the PC/rGO and PAHs, including hydrophobic and π-π interactions, partitioning, and mesopore filling effect. In the analysis of PAHs, the PC/rGO fiber showed a wide linearity (0.007-100 ng mL-1), low limits of detection (0.0005-0.005 ng mL-1), and good repeatability (RSDs <10.1%, n = 5) under optimized conditions. The established method was applicable for ultrasensitive determination of PAHs in different environmental waters and showed satisfactory recoveries. This study provides a novel way for constructing thermally stable SPME coating having efficient extraction performance.

Self-Healing Hydrogel Membrane Provides a Strategy for the Steady Production of Clean Water from Organic Wastewater

When the typical solar-driven hydrogel water evaporator treats the organic sewage, the organic pollutants will be accumulated in the evaporator and affect the evaporation performance. This issue is resolved by using silver-disulfide bonding to fix the silver oxide/silver (Ag₂O/Ag) nanoparticles inside the polyacrylamide-acrylic acid hydrogel, resulting in the photocatalytic degradation of methyl orange and solar-driven water evaporation. Ag₂O/Ag nanoparticles are a solar-thermal conversion material used to replace the traditional carbon material. On the one hand, the heterojunction structure of Ag₂O/Ag enhances the separation ability of the photogenerated carriers, thereby increasing the photocatalytic efficiency. On the other hand, the surface of the nanoparticles is grafted with N, N'-bis(acryloyl) cystamine and becomes the crosslinking agent which is fixed in the hydrogel. Meanwhile, the inverted pyramid structure can be built at the surface of the hydrogel by soft imprinting technology. This kind of structure has excellent light trapping performance, which can increase the efficiency of Ag₂O/Ag photocatalysis. Furthermore, the dynamic reversible coordination effect between Fe³⁺ and carboxyl realizes the self-healing capability of the hydrogel. Here are the properties of hydrogel: the fracture stress is 0.35 MPa, the fracture elongation is 1320%, the evaporation rate is 1.2 kg·m^-2·h^-1, and the rate of the photocatalytic degradation of methyl orange is 96% in 3 h. This self-healing hydrogel membrane provides a strategy to steadily get clean water from organic sewage.

Removal of Hg2+ in wastewater by grafting nitrogen/sulfur-containing molecule onto Uio-66-NH2: from synthesis to adsorption studies

The remediation of heavy metal deserves to be on the agenda, with the adsorbent design bearing the brunt of it. In this study, the molecule (4, 6-diamino-2-mercaptopyrimidine, DMP) containing thiol (-SH) and amino (-NH₂) functional groups was grafted onto Uio-66-NH₂, and a composite metal-organic framework nanomaterial (Zr(NH₂)-DMP) was synthesized via a facile post-modification scheme. The morphological characteristics and structural features of the modified adsorbent were characterized by XRD, FT-IR, FE-SEM, EDS, BET, and XPS. The characterization results verified that the post-modification scheme was successfully achieved. The adsorption experiments were carried out to investigate the removal performance of the Zr(NH₂)-DMP towards Hg²⁺ under different influencing parameters. The maximum adsorption capacity of 389.4 mg/g was obtained, and the adsorption equilibrium was achieved within 30 min at pH 6 at room temperature. Adsorption thermodynamic study indicated that the adsorption process was exothermic and spontaneous. The Zr(NH₂)-DMP exhibited excellent selectivity for Hg²⁺, and also has the potential to remove Cu²⁺, Fe²⁺, and Zn²⁺ ions. The introduction of Cl^- inhibited the removal of Hg²⁺ due to the formation of mercuric chlorides (removal efficiency reduced from 97.8 to 95.6%). The removal efficiency of up to 86.7% was obtained after four cycles. The Langmuir isotherm and Pseudo-second kinetic were more suitable for fitting the adsorption process of Hg²⁺ by Zr(NH₂)-DMP. The main removal mechanism could be attributed to the chelation between Hg²⁺ (soft acid) and nitrogen/sulfur (soft base) elements. These findings convinced that the successful synthesis of Zr(NH₂)-DMP provides an option for Hg²⁺ removal from wastewater.

Reed Rhizome Residue-Based Activated Carbon Adsorption Ultrafiltration Membranes for Enhanced MB Removal

Novel adsorption ultrafiltration (ADUF) membrane was designed for the removal of methylene blue (MB) by introducing Chinese herbal waste-based activated carbon (AC) into the ultrafiltration membrane. We prepared AC particles from Chinese herbal medicine waste residue (reed rhizome residue) as a raw material by ZnCl₂ activation and introduced them into the ultrafiltration membrane by phase inversion to prepare a reed rhizome residue-based activated carbon adsorption ultrafiltration (RAC-ADUF) membrane. The RAC-ADUF-0.1 membrane was characterized by a series of physical structures and chemical properties, which showed that the prepared membrane has a more hydrophilic surface and high porosity. The RAC-ADUF-0.1 membrane showed an excellent pure water flux of 255.77 L·m^-2·h^-1 and a high bovine serum albumin rejection of 99.3%. The RAC-ADUF membranes also possessed excellent antifouling performance. Notably, the RAC-ADUF-0.1 membrane provides excellent removal of MB (99% retention) compared to conventional ultrafiltration membranes. The static adsorption capacity was up to 238.48 mg/g. The significant increase in dynamic adsorption capacity on the RAC-ADUF membrane is due to the three-dimensional distribution of RAC particles on the PSF membrane cross section, which provides more active sites and increases the contact time between RAC and MB. By fitting the adsorption kinetics and isothermal adsorption curves, the results showed that the pseudo-second-order kinetic model and the Langmuir isothermal model were more accurate in explaining the adsorption process. Further kinetic analysis showed that the adsorption process of MB molecules on RAC-ADUF membranes is controlled by both external mass transfer and intraparticle diffusion, with intraparticle diffusion playing a dominant role. In addition, the RAC-ADUF membrane exhibited outstanding adsorption and regeneration abilities, and the MB removal rate stayed at about 95% after 8 adsorption regeneration experiments. In conclusion, this study provides a new idea for the preparation strategy of an adsorption ultrafiltration membrane with high rejection and high permeability and the reuse of Chinese herbal medicine waste residue.